Which muscle is affected in a patient with trismus?

Trismus refers to limited mouth opening, often caused by spasm or inflammation of the medial pterygoid muscle, which is involved in closing the jaw. Conditions such as infections (e.g., pericoronitis), trauma, or temporomandibular joint disorders can lead to trismus. Buccinator is involved in facial expression and food manipulation, not trismus. Lateral pterygoid is involved in opening the jaw and lateral movements. Masseter aids in jaw closure but is less frequently implicated in trismus.